Table of Contents


A completely open design for a function/waveform generator: hardware, firmware, software

for more info, read about openbench

For collected links, try DDS link on delicious and Function Gen link on delicious

Notes & stuff

Design constraints

One or two designs: Low cost, high cost.

Waveforms we want (in order of importance)

Modulation (in order of importance)

Frequency range:

Output capabilities:

USB control? Serial control? Panel control? All of the above?

Vpp? (+-12V is pretty 'standard')

100mA is not a bad current capability to shoot for

PCB is doublesided, 10/10 rule

Parts are DIP, thruhole or PLCC (preferred) SOIC, 1206 (likely). No TSSOP, QFP, LLP, MSOP, uSOIC, etc.

Waveform generation

Waveforms we want (in order of importance)

Frequency range:

Generator tech

Two options for chip 'styles' is the all-in-one oscillator (ICL3038, etc) +PLL or DDS


All-in-one is nice, although not very stable w/o PLL. Two options available, MAX038 & XR220.

Pros: easy, cheap, simple Cons: unavailable, PLL required


Direct-Digital-Synthesis, currently popular. Basically: wavetable + 24 or 32 bit adder and sampling above nyquist to get precision waveforms.

Either roll your own or buy off the shelf (basically from AD)

Off the shelf, AD parts

They come with sync out, very very high speeds. But only sine and square out, and in small packages (TSSOP).

Roll your own

Idea #1: Get a chunk of SRAM (like, say, CY7C1399B-12VXC), fill it with your wavetable, then clock it with a variable clock (LTC6903 1KHz→68MHz !!) maybe use along with adder/scaler to provide more range at high/low freq. We could get up to 4MHz, nice!

Idea #2: SRAM + 32 bit adder, just like AD. Maybe make the adder in a CPLD or something else that can be clocked super-fast (See ELM's DDS generator)

Look at: , a handmade adder

For CPLD, 100MHz PLCC (44 or 68) either XC9500 (xilinx) or MAX7000 (altera)

Idea #3: Hand-roll the adder code into an AVR microcontroller, and use onboard memory. Lots of examples: AVR generator or Jesper miniDDS (note: can't we do this in 8 cycles by using LD? just make sure we have an AVR with more than 256b of RAM)

Other possibilities include going with an SX instead of AVR: SX28 can be clocked up to 75MIPS (maybe give us 500KHz…but will draw an insane 100mA from 5V. jesus!)

Idea #4: A combination of idea #1 and idea #3. Take a simple AVR that is able to calculate waveforms, but not in realtime. Load the wavetable in some external RAM, and clock it at the desired speed.

Power supply

Need 3.3V (probably), 5V, +-12V (@100mA)

Idea #1 Use 'computer' power supply: $5-$10!

Idea #2 Use 78xx's with mains transformer.

Idea #3 Use a regulated power supply/wall wart with multiple outputs (see Jameco#154624 5V @0.5A +-12V @0.13A each $13)

Idea #4 DC/DC converters, run off of 'single' supply like 5V or 9VDC

Idea #4b Build your own DC/DC converter, a bit like sprite_tm did. Have the processor generate the PWM needed for the converter.

Planned versions

Inexpensive kit


USB and/or external power (9VDC)

Single output, +12V max (maybe -12V too).

Boost converter: LT1610 will give +12V @ 1.2MHz switching freq. Has 8V max input so must clamp input. ugh.

For isolation, use wall wart that provides 5→9VDC


2x16 LCD and some buttons & rotary encoders for UI. Maybe an 'm88? at 12MHz does the UI work and USB nonsense. (USB "serial" (or raw) interface using USBtiny.) and sends just raw serial/spi commands to DDS chipset


DDS done by dedicated chip probaby Atmega48 running @ 20MHz

DAC is DAC0800 (?)